1. Field of the Invention
The present invention relates to fusible link memories, more particularly to lateral polysilicon programmable read only memories.
2. State of the Art
Programmable Read Only Memories (PROMs) have their roots in early bipolar technologies using various metal films as the programmable element (fuse). These early PROMs used the inherent high current characteristics of bipolar transistors to deliver sufficient current in the metal fuse such that metal migration would occur, causing an open circuit in the fuse. These metal fuses typically required extra masks and process steps to achieve thin cross sections in order to minimize the amount of current to open the fuse.
The destructive fuse eventually was replaced with non-destructive, CMOS, electrically erasable elements that could be programmed multiple times, with essentially no yield loss.
EEPROMS are PROMs using electrically eraseable (EE) cells. Although EEPROMS are very high yielding, they typically require several extra mask and process steps to manufacture, adding significantly to the final cost of a basic logic process flow. EEPROMs therefore are manufactured as high yielding, high density products requiring dedicated process flows and fabrication facilities.
There are a number of applications where only a small number of bits of non volatile memory would be beneficial. These benefits can be offset, however, by the large cost of adding an expensive memory flow to the technology being used. It would therefore be beneficial to construct a non volatile memory cell requiring no extra process steps.